Aircraft flight operations may involve flight patterns that occur in close proximity to the ground. Helicopter flight operations, in particular, typically involve a significant amount of flight time in close proximity to the ground. This is particularly true of military helicopters with the advent of more sophisticated avionics and flight equipment that make nap-of-the-earth flight operations feasible as a routine tactical flight philosophy.
Helicopter flight operations in close proximity to the ground are subject to two serious types of ground threats: gun fire (active); and wire/cable strikes (passive). These ground threats have become a serious concern with the increasing emphasis on nap-of-the-earth helicopter flight operations.
During the Vietnam War, many helicopters were neutralized or destroyed as a result of encounters with steel cables stretched between trees. Such cables were purposely positioned to wrap around the helicopter rotor head to disable the helicopter, or, if the speed of the helicopter was sufficiently high, to tear through the helicopter fuselage for complete destruction thereof.
To mitigate this liability in low level helicopter flight operations, wire cutter systems were developed and incorporated into the basic helicopter configuration. Such wire cutter systems are operative to deflect wires/cables encountered during low level flight operations into the throat of a wire cutter. The momentum of the helicopter, in combination with the sharpness of the cutter blades, is sufficient to sever wires/cables before damage can be inflicted upon the helicopter.
Wire cutter systems are currently utilized on helicopters engaged in low level flight operations where there is a high probability of encountering wires/cables. For example, almost all military helicopters incorporate wire cutter systems. In addition, federal and state helicopters utilized in illegal alien operations typically incorporate wire cutter systems. It is not uncommon for such helicopters to strike numerous telephone and/or power lines while engaged in illegal alien flight operations. Telephone and/or power lines in themselves are not the primary concern, but rather the steel cables (up to three eights inch diameter) that are disposed in combination with such lines for the support thereof. These steel cables are similar to the type encountered by helicopters during the Vietnam War.
Wire cutter systems must be effectively designed and utilized to sever such support cables. One limitation of prior art wire cutter systems is that each cutter system is fixedly mounted in combination with the helicopter. Hence, each cutter system is only effective in protecting helicopters from wire/cable strikes over a limited strike zone.
To overcome this limitation, many wire cutter systems incorporate a deflector member that is operative to direct/deflect encountered wires/cables into the jaws of the cutter. The placement of these deflector members, therefore, is extremely critical if the wire cutter system is to have the capability to provide maximum protection for the helicopter.
A special problem arises for helicopters having external, belly-mounted gun systems. The gun system and the belly of the helicopter in combination form a crevice that defines a critical strike zone capable of entrapping wires/cables that may severely damage the belly-mounted gun system and/or the helicopter. If the gun system is capable of pivoting motion in the elevational plane, the critical strike zone defined by the helicopter and the gun carriage in combination becomes extremely large. For example, the AH-64 Apache helicopter incorporates an external, belly-mounted gun system having the capability of pivoting motion in the elevational plane. In consequence, the Apache helicopter employs multiple fixed cutters and deflector members to protect the critical strike zone defined by the external, belly-mounted gun system and the lower fuselage of the helicopter from wire/cable strikes.
More specifically, the Apache helicopter requires two wire cutter systems just to protect the belly-mounted gun system: one belly-mounted wire cutter system and one wire cutter system fixedly mounted on the gun. The belly-mounted wire cutter provides effective protection against incident wires/cables that slide along the lower fuselage of the helicopter. The gun-mounted wire cutter provides effective protection against incident wires/cables that impact the gun below the mounted wire cutter. Thus, while these wire cutter systems are generally effective in protecting the gun system and helicopter from wire/cable strikes under certain conditions, a large unprotected strike zone still exists if the gun system is pivotally positioned in other than the stowed flight condition, i.e., the gun system is in a depressed position. In addition, the need to provide multiple wire cutter systems results in a system weight penalty.
A need exists to provide a lightweight wire cutting system for helicopters (and other types of low flying aircraft) that embody external, belly-mounted gun systems, especially those having guns capable of pivoting motion in the elevational plane. Such a lightweight wire cutting system should be configured to minimize the number of individual wire cutters and deflector members while concomitantly providing maximum protection from wire/cable strikes for the critical strike zone defined by the pivotal range of the external, belly-mounted gun system.